The invention relates to drilling machines, and more particularly, to drilling machines having a feed cable tensioner.
Drilling machines typically include a frame, a tower, and a rotary head. The frame is supported for movement over the ground, and the tower is mounted on the frame. The rotary head is movable along the tower and engageable with the drill string for rotating the drill string.
Feed cable systems are connected to the rotary head to position and direct forces to the rotary head and drill string during drilling operations. For example, the feed cable system moves the rotary head downward to force the rotating drill string into the ground to drill a hole and upward to raise the drill string out of the drilled hole.
The feed cable system includes a cable and pulley assembly that is connected to an actuator. Movement of the actuator in a first direction applies tension to a pull down cable to provide a downward force on the rotary head and movement of the actuator in the opposite direction applies tension in a pull back cable to provide an upward force on the rotary head. Feed cable systems have many advantages over other systems, however, the cables of the feed cable system stretch under load. Further, the pull down and pull back cables on known the cable system are configured such that cable stretch in one of the cables caused by the tension applied to the cable results in a corresponding slack in the other cable.
Slack experienced in the cables is disadvantageous because loose cables in a cable and pulley system are likely to disconnect from the pulleys and cause the cable to whip from the pulley when a tension is reapplied to the loose cable. In addition to requiring immediate maintenance to repair the feed cable system, cable whip is capable of causing injury to vehicle operators and damage to surrounding equipment on the drilling machine.
The feed cable system of the present invention prevents loose pullback cables by including take-up cylinders that remove slack from the pullback cables when the pull down cables experience elastic stretch. The take-up cylinders increase the safety of the operation of the drilling machine because loose cables have the potential to disconnect from pulleys and sheaves which could cause substantial damage to surrounding equipment from cable whip.
One embodiment of the present invention is directed to a drilling machine for use with a drill string. The drilling machine also includes a pull down cable, a pull back cable, and a slack take-up device. The pull down cable is connected to a rotary head for pulling the rotary head downward relative to a tower for pushing the drill string into the ground. The pull back cable connected to the rotary head for pulling the rotary head upward relative to the tower for pulling the drill string out of the ground. The pull back cable is subject to a slack condition in response to elastic stretch of the pull down cable. The slack take-up device is connected to the pull back cable to remove the slack created in the pull back cable by the elastic stretch of the pull down cable.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.